Canker Sore

August 22, 2016

A 32-year-old man visits the ED for an oral canker sore that should have run its course but is getting worse. What one question should you ask?

A 32-year-old male presents to the emergency department for a painful cold sore that he has had for about three weeks, and that is not getting any better. He previously went to an urgent care near his work where they diagnosed him with a canker sore. He was directed to take ibuprofen and told the lesion would probably go away in a week or two, but it has been more than 2 weeks and he feels he is continuing to get worse with pain now spreading into his throat. He denies any fever, vomiting, runny nose, or other complaints. He says he has cold sores before, but never like this.

On physical examination his vital signs are all within normal limits and he is in no acute distress without stridor, drooling, trismus, or abnormal voice. Images of his throat are shown below with the canker sore just posterior and medial to his left mandibular wisdom tooth on the edge of his tonsillar pillar.

A CBC is normal except for 38% atypical lymphocytes.

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What diagnosis should you worry about and what critical question should you ask the patient?

Please click here for answers and discussion.

Answers: You should worry about syphilis. And, you should ask the patient if he is sexually active, if he has had oral sex in the last 2 months, and particularly if he has been with any new partners.

Diagnosis: Oral syphilitic chancre



Most oral ulcers are aphthous ulcers, also known as canker sores, and are benign idiopathic painful sores usually less than 1-cm in diameter that usually last 1-3 weeks. Ulcers that are larger than 1 cm or last more than 3 weeks are often due to a specific disease and should be investigated. Causes include viruses such as HSV or HIV, inflammatory conditions such as lupus, Crohn disease or Behcet’s and other conditions (more information on oral ulcers in Table 1  below). In this case there was suspicion for syphilis, which was heightened when the history of recent oral sex with a new partner was elicited.

Oral syphilitic chancres, unlike genital chancres, are often painful. This patient was treated empirically with penicillin IM and an RPR was ordered. In addition, a CBC was ordered which showed an elevated atypical lymphocyte count. Causes of atypical lymphocytes include drug reactions and a number of infections, the most famous being the causative virus for mononucleosis. Other infectious causes of atypical lymphocytosis include the following: CMV, toxoplasmosis, syphilis, group B Strep, hepatitis C and hantavirus (for other causes see Table 2 below).

Remember the rule of 3’s for primary syphilis. It has an incubation period of up to 3 months but averaging 3 weeks. Ulcers are usually 0.3- to 3-cm in diameter and persist for 3 to 33 days or more. Genital ulcers are often painless but ulcers elsewhere may be painful.

The initial RPR was negative in this patient, but it is important to be aware that in a first syphilis infection, antibody tests like RPR often take 4 weeks or more to turn positive, even up to 8 weeks at times. His repeat RPR 2 weeks later was positive. Testing for syphilis is somewhat complex and the details are beyond the scope of this article but it is important to know that the RPR can be falsely negative in early or late disease and falsely positive in a variety of autoimmune conditions. It is a quantitative test so titer levels can be followed. A four-fold drop in titer usually signifies a cure.


Table 1. ORAL ULCERS from ENT chapter of Quick Essentials Emergency Medicine pocketbook

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Table 2. ATYPICAL LYMPHOCYTES from Lab chapter of The Emergency Department Quick Reference Guide

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For additional information, click on images below.

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